fix(types): add walkUniversal declaration (#311)

Author: marcalexiei

postcss-selector-parser.d.ts

@@ -263,6 +263,7 @@ declare namespace parser {
             callback: (node: Pseudo) => boolean | void
         ): boolean | undefined;
         walkTags(callback: (node: Tag) => boolean | void): boolean | undefined;
+        walkUniversals(callback: (node: Universal) => boolean | void): boolean | undefined;
         split(callback: (node: Child) => boolean): [Child[], Child[]];
         map<T>(callback: (node: Child) => T): T[];
         reduce(

postcss-selector-parser.test.ts

@@ -2,11 +2,18 @@ import * as parser from './postcss-selector-parser';
 
 parser((root) => {
     root.each((node, index) => {
-        node as parser.Selector;
-        index as number;
+        node satisfies parser.Selector;
+        index satisfies number;
     });
     root.walk((node, index) => {
-        node as parser.Selector;
-        index as number;
+        node satisfies parser.Node;
+        index satisfies number;
+
+        if (node.type === 'selector') {
+            node satisfies parser.Selector;
+        }
+    });
+    root.walkUniversals((node) => {
+        node satisfies parser.Universal;
     });
 }).processSync("a b > c");